Pertussigen (pertussis toxin) (Ptx) is an extremely active toxin affecting various immunological related phenomena. Thus it increases the number of leukocytes, the susceptibility of mice to anaphylaxis and histamine shock; it enhances the induction of experimentally induced autoimmune diseases, has a mitogenic action on T-lymphocytes and enchances markedly the production of IgE and, to a lesser extent, other immunoglobulins as well. In this project, we studied the effect that Ptx has on different lymphocyte populations including the effect on lymphocytes containing IgE on their surface. We found that in the blood, Ptx increased markedly the number of both B- and T-lymphocytes which included the Lyt1+ (helper) and the Lyt2+ (suppressor) lymphocytes. However the most striking effect was the increase in the percentage of B-lymphocytes starting one day after Ptx injection. In the spleen lymphocytes, only a small decrease in the number of B-lymphocytes was observed, although the percentage of all T-cells decreased slightly from the second to the ninth day after Ptx. Ptx induced a marked increase in the IgE containing cells both in the blood and the spleen. This increase was as high as ten-fold that of normal values. With whole cell vaccines made from mutants of B. pertussis lacking all or part of the Ptx gene it was found that any modifications of the portion of gene responsible for the production of the S-1 subunit of Ptx made the vaccines inferior in producing lymphocytosis, histamine sensitivity, stimulating IgE or enhancing anaphylaxis. Furthermore, the ability of these vaccines to induce protection against intracerebral challenge was markedly decreased. These studies will be continued during the following year.